1. Field of the Invention
This invention relates to portable locators that sense electromagnetic emissions to thereby locate buried utilities such as pipes and cables.
2. Description of the Related Art
There are many situations where is it desirable to locate buried utilities such as pipes and cables. For example, before starting any new construction that involves excavation, worker safety and project economic concerns require the location and identification of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.”
As used herein, the term “buried objects” includes objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, for example, as well as objects disposed below the surface of the ground. If excavation equipment such as a backhoe hits a high voltage line or a gas line, serious injury and property damage may result. Unintended severing of water mains and sewer lines generally leads to messy and expensive cleanup efforts. The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to business. Therefore man-portable locators have been developed that sense electromagnetic emissions to thereby locate buried utilities such as pipes and cables. This is sometimes referred to as “line tracing.” If the buried cables or conductors carry their own electrical signal, they can be traced by detecting the emissions at their appropriate frequency. Often signals with a known frequency are applied to pipes and cables via a transmitter to enhance the ease and accuracy of the line tracing. This can be done with an electrical clip in the case of a pipe, or with an inductive coupler in the case of a shielded conductor. Sometimes sondes are used to trace the location of pipes. These are tiny transmitters that are inserted into a pipe and emit electromagnetic signals at a desired frequency.
Portable utility locators typically carry one or more antennas that are used to detect the electromagnetic signals emitted by buried pipes and cables, and sondes that have been inserted into pipes. The accuracy of portable utility locators is limited by the sensitivity of their antennas. Signal interference caused by capacitance or inductance within the antenna structures causes resonance and interference. Additionally, methods of processing signals detected by antennas in portable utility locators by amplifying them and mixing them, have traditionally suffered from inefficiencies which include vulnerability to radio-frequency interference (RFI) and electromagnetic interference (EMI), and the introduction of undesirable capacitance and inductance.
Accordingly, there is a need to improve the sensitivity of antennas used in human-portable locators while improving their performance in isolating and processing signals of interest, and reducing circuit complexity and cost.